Cognitive Neuroscience: A Very Short Introduction

A Recent Field

• Visualization Techniques:
  • PET (Positron Emission Tomography) - 1980s
  • fMRI (Functional Magnetic Brain Imaging) - 1990s - the ratio of oxygenated to de-oxygenated blood.
• Help us learn about:
  • Human capacities
  • Human limitations
  • Disorders of the nervous system

Perceiving

• Lateral Occipital (LO) complex - an area that is activated when people recognize objects. Critical for the ability to use the ahape and orientation of an object to guide the way in which the hand approaches it.
• Information from vision, hearing, touch, and smell is relayed to from the sense organs to separate regions of the brain, which are referred to collectively as the primary sensory areas:
  • V1 - the primary visual area, with secondary areas V2, V3, V4, etc. The primary visual cortex relays information via these and other areas to the temporal lobe and the parietal lobe. These relays are termed the ventral and dorsal visual pathways.
• The brain has a parallel architecture with some choke points
• Localization of function - the brain is a patchwork of discrete areas. Each area consists of a host of neurons arranged in six layers, each layer being many neurons thick. The areas differ in the thickness of the layers, the density of the packing, and the frequency of the different types of neuron.
• The incoming connections determine the information that the area can process, the outgoing connections determine the influence that it can exert on other areas.
• The outside world is mapped onto the brain in a point-to-point fashion. The primary somatosensory area (S1) is a map of the body with different parts responding when the hands, body, or legs are touched. In the primary visual cortex (V1) there is a retinotopic map - the retina is mapped onto the cortex such that the location of the activity in the cortex depends on which part of the retina is stimulated by light.
• Because we use our hands for manipulating objects, much more tissue is devoted to the hand than to the foot. In the V1, more tissue is devoted to central than peripheral vision. In the centre of the eye there is a pit or fovea and it is here that there is the greatest density of light receptors. When we inspect an object is is with the fovea that we focus our gaze.
• Integration between sensory modalities is achieved by connections to common reas, and these are referred to as "multimodal" areas, including the parietal cortex and the prefrontal cortex. These areas are multimodal because they can be activated irrespective of whether the stimuli are visual, auditory, or tactile.
• Processing occurs via successive stages in the visual relay. The earlier stages process the elements and the later stages integrate them via a hierarchical arrangement in which each higher-order neuron in area B receives an input from many lower order neurons in area A, and so on up through the stages.
• Lower-order neurons respond maximally when we see an object from a particular view whereas higher-order neurons integtrate the information from lower order neurons and are thus able to learn to respond irrespective of the view to let us form a view-independent representation of the object.
• As a child we are taught that different animals are primates or birds. The suggestion is that the representation of these categories is learned by groups of neurons in higher areas through the association of inputs from lower-order areas.

Attending

• At any time you are only interested in some of the information that is available. This is particularly true for what we see.
• Activation is greater when attending than when not doing so in two regions - the intrapiarietal sulcus and the frontal eye field (the dorsal attention system). Both areas are also engaged when people actually move their eyes or simply plan to move their eyes. When you attend to the periphery while gazing centrally, the enhanced activation reflects the fact that you are preparing to move your eyes.
• No behavioral process depends on a single area of the brain - activations are distributed across the brain. So anatomical systems support functional systems.
• An object catches our attention either because it is salient or because we are looking at it. In either case, if the object is in peripheral vision we move our eyes so as to bring it into central vision.
• In spatial neglect, eye movements are almost entirely confined to the right hand side of the display. Neglect most often results from strokes that involve the right parietal cortex. In a stroke the blood supply to an area is cut off, either because of a blockage or leakage in an artery. The effect is that the neurons in the area that is supplied by that artery die through lack of oxygen and glucose.
• The inferior parietal cortex and the temporo-parietal junction (TPJ) form part of the ventral attention system. The TPJ forms a critical node at which the temporal and parietal cortex can interact.
• Target detection tasks provide one situation where that interaction is required. The ventral visual stream is involved because the letters are identified on the basis of their shape; and the parietal cortex is involved because some of the targets will appear in peripheral vision.
• If a large stroke affects the left parietal cortex, the right inferior parietal cortex and TPJ are still available for detecting targets whether they appear on the left or the right. But after a large parietal lesion on the right, the left parietal cortex can only support detection of targets on the right.
• Mental distraction led to a decrease in the activation in the sensory pathway in the spinal cord, and the people also reported that they felt less pain. The signals that cause this reduction originate in the prefrontal cortex. It sends top-down signals that appear to evoke a release of opiates in the system and it is this release that moderates the pain.
• The fusiform face area (FFA) is involved in the discrimination of faces.
• Top-down signals can:
  • Set up a task by enhancing processing in the relevant sensory stream.
  • Set up the targets by creating a template against which they can be matched.
  • Inhibit processing in irrelevant input streams.
• The ventral prefrontal cortex transforms sensory input into motor output. If it is to transform any input into any output it needs a matrix of interconnecting neurons so that routing through the area allows for maximum flexibility.

Remembering

• Unlike small objects, which we can fixate in central vision, scenes are extended and so they fill our visual field. The parahippocampal cortex is activated if people are scanned while they view pictures of scenes or large objects such as houses that could serve as landmarks
• The hippocampus represents where we are, and people with damage to it have trouble finding their way around.
• Why does an animal want to remember a place? Because that is where they saw food, a mate, or their offspring. But the world changes, so it pays animals to know not only where they last saw these things, but also when.
• During recall, the hippocampus, retrosplenial cortex, posterior cingulate cortex, and the medial and inferior parietal cortex are activated to provide a feeling of reinstatement or the subjective feeling of reexperiencing the event
• The hippocampus provides the spatial context for events, whether the context is actually present or only there in the imagination. The events are autobiographical or personal because we were present at the time. And recall depends on the process of reinstatement in the cortex. It is this that we experience as reliving the event.
• In the case of semantic knowledge there is activation in the middle and inferior temporal cortex extending to the perirhinal cortex, which lies at the temporal pole. There is also activation in the ventral prefrontal cortex with which these are connected. The activations in common for pictorial and verbal questions are all in the left hemisphere, which is specialized for language.
• There is a clear distinction between a medial system for remembering events in our life, and a ventral and lateral system for knowledge concerning objects. The perirhinal cortex is concerned with object-specific semantic information and it is increasingly engage as the number of semantic features that objects share increases. Damage to it can lead to problems in naming things and the problems become worse, the more they are perceptually and semantically confusable.
• Remembering personal names is one of the most taxing semantic tasks and is particularly sensitive to ageing. Seven years before there is a severe memory problem with alzheimers, it is possible to detect a loss of colume in the hippocampus.

Reasoning

• Non-verbal tests like Raven's Matrices activate the parietal and dorsal prefrontal cortex. They provide the most reliable assessment of general intelligence (g). Patients with lesions in the temporal lobe are unimpaired on tests using shapes or symbols, but those with parietal or prefrontal lesions are.
• These regions hold information about spatial relations - the parietal cortex is specialized for the representation of space. There is a relation between space and distance, and judgements for letters or numbers are made on the basis of the distance apart in the series.
• There are relations between size, distance, and number and thus the parietal cortex is needed
• Broca's area (B) and Wernicke's area (W) are both part of the phonological (as opposed to the semantic) system. If you speak silently to yourself, there are activations in both B and W, so it is like we are hearing ourselves speak.
• But language is not necessarily used in logical thought. Logic depends on relations such as esuqlity or difference, larger than or smaller than, and these relationships are managed by the parietal cortex.
• General intelligence depends on the executive control system in the prefrontal cortex.
• We don't really think in language, but children are taught in language and told about the properties of objects and how to categorize them. In this way, abstract semantic concepts and the relations between them are explained in language.
• We inherit both our genes and our knowledge and understanding (via culture) from previous generations.
• Comparing the chimpanzee brain to the human brain:
  • The areas involved in producing and understanding spoken language (B and the non-primary auditory cortex in the superior temporal gyrus) are expanded
  • The most dramatic change is in the prefrontal cortex and the frontal pole - proportionally twice as big in humans.
  • There is much more tissue in the human brain for processing semantic knowledge about objects and for analyzing spatial and other relationships.
• Language is for communication, not thought.

Deciding

• The prefrontal cortex is at the top of the hierarchy of processing
• It receives input from all sense modalities and so is in a position to form a multimodal representation of the current situation in the world outside, from:
  • The inferior temporal cortex for vision
  • The superior temporal cortex for hearing
  • The secondary somatic sensory area in the parietal lobe for touch
  • The inferior parietal lobe for visual space
• It is informed of current needs by:
  • The orbital prefrontal cortex, which is connected to
  • The amygdala which is interconnected with
  • The hypothalmus, which is responsive to changes in hunger, thirst, and temperature.
• It can influence actions via direct connections with the premotor areas that connect in turn directly to the motor areas
• It can specify the relative values of potential choices, based on an abstract scaled of value, so it can compare the value of different types of rewards.
• It makes possible the moment-to-moment flexibility that is characteristic of human (and primate) behavior in general. In our complex physical and social world, by paying attention to each situation, we can decide what is or is not appropriate - our behavior is under "attentive control".
• But certain skills become automatic and habitual. When learning a new skill there is at first much activation in the dorsal prefrontal cortex as we work by trial and error, but as training goes on it diminishes, and activation moves to the following closely interconnected areas:
  • The posterior part of the striatum
  • The medial parietal cortex
  • The supplementary motor cortex and the motor cortex.
• Habits are efficient, but lapses can occur when habitual actions are run off at moments when they are no longer appropriate. The situation has changed and the prefrontal mechanisms will need to be re-engaged - we need to think about what we are doing once again.
• When waiting to act and holding information in "working memory" there is activation in the parietal cortex instead of the prefrontal cortex.
• But when preparing to act, the prefrontal cortex is activated - we are preparing, planning, working out what to do, and deciding.
• And when checking what we have done, the intraparietal sulcus is activated.
• The evolutionary advantage of being able to try out ideas in the head is that it is possible to image int epotential outcomes and thus avoid those that are bad. ie humans can do "mental trial and error", which involves an ability to image the outcomes.
• But our imagination is less detailed and so we tend to overvalue non-immediate outcomes. Those who can wait show activation in the ventromedial prefrontal cortex. Similarly, when making a risky choice, the more activation in the ventromedial prefrontal cortex the more success in avoiding the risky path.
• Compulsive gamblers have less alertness than others and take more risks and tend to overvalue immediate rewards despite the dangers of long-term losses.
• The ventromedial cortex is also involved in imagining outcomes with emotional valence. It is activated when people think of how others would feel about emotional situations. Damage to this area leads to stealing lying, and being impervious to punishment, and lacking a sense of guilt.

Checking

• The brain monitors and regulates itself, not some other ghostly presence.
• Introspection tells us that when we deliberate we are aware of doing so, but it is difficult to base a scientific account on subjective report.
• In the "Libet Task" it was proved that before a voluntary action there is brain activity of which we are unaware - it appears to show my brain dictating to me.
• It is wrong to characterize the situation as "me" vetoing what my brain was planning to do.
• Monitoring performance is specially important when the task is difficult and there is a danger of making mistakes.
• Activation in the anterior cingulate cortex is particularly marked when people detect errors they have committed.
• When you detect an error, you want to do things right next time. The greater the activation in the anterior cingulate, the greater the degree to which the dorsal prefrontal cortex is re-engaged during the next repetition of the task.
• When watching others and determining their intentions, there is activation in the temporo-parietal junction and in the rostral part of the anterior cingulate cortex:
  • The TPJ activation is related to whether the movements were unexpected - it receives information about motion and in particular "biological motion" - the coherent motion of limbs and body.
  • The rostral cingulate cortex activation is related to the accuracy of the judgements about whether the actor was or was not trying to deceive, activating when the observers were correct about his intentions. This same activation is seen when understanding jokes based on the intentions of people.
• Mentalizing or inferring the thoughts and intentions of others is based on two methods:
  • Mirror neurons - when observing others doing odd things, there is activation in the ventral prefrontal cortex, suggesting covert simulation.
  • Using semantic knowledge about how people behave to interpret their actions. When there is attention on the intentions of the others there is activation in the rostral cingulate cortex, suggesting reflecting on mental states
• Reflecting on the intentions of others involves metacognition or thinking about thinking.
• The medial surface concerns the self and there is a posterior to anterior organization of it. There is activation:
  • Near the Pre Supplemental Motor Area when we attend to our intentions.
  • In the anterior cingulate cortex when we monitor our responses.
  • In the rostral cingulate cortex relating to the movements of others, so the activations are more anterior when we mentalize or empathize with the feelings of others.
  • In the medial prefrontal cortex when we reflect on past or future events.
• Metacognition involves representing a representation (thinking about thinking), so a way to do this could be via a hierarchical organization and the increase in size of the human anterior cingulate cortex may reflect the addition of more layers to the hierarchy.

Acting

• Differences with other primates:
  • We are much more able than other primates to move each finger independently
  • The majority of people prefer to use their right hand for skilled actions such as writing or throwing.
  • There is a relation between handedness and speech.
• Right-handedness goes back as far as 1.5m years, probably related to early tool making.
  • There is a clear advantage in training up one hand, as it takes long practice to acquire, and this way it is always the same hemisphere (opposite to the hand) that learns, and there would be a tendency towards increasing standardization over the generations.
  • Handedness probably came long before spoken language (70k-100k ya), but hominins probably used gestures for communication before speech. This is why the left hemisphere would be involved, because of the tendency to right-handedness. A specialization for gestural communication would have formes a pre-adaptation for spoken language. In modern humans, the left hemisphere is critical for gestural communication
• There is activation in the left inferior parietal cortex when observing gestures as this is about judging and comparing biological motion. And this area connects directly to Broca's area, and the connection is more extensive, for humans, in the left than the right hemisphere
• In the human brain there are also connections to B from W in the superior and middle temporal gyrus with these connections favoring the left hemisphere. So B has access to information about gestures as well as about the sounds of speech.
• When people have left hemisphere stokes, they often have problems with language and with imitating gestures
• Broca's area seems to form a common hub between the gestural and vocal systems.
• Skills - involve precision in the application of force, in the control of rhythm, and/or in the coordination of different movements, and once these are acquired, we see activation in the cerebellum at the base of the brain.
• The cerebellum is also involved in language skills, and damage to it impacts both manual and vocal skills.
• The cerebellum is dramatically expanded in the human brain and is interconnected with the cortex.
• As people learn manual skills, the sensory consequences of the movements become more predictable. But if unexpected things happen there is a signal (or prediction error) in the cerebellum.
• This prediction error is similar to the signal in the anterior striatum associated with measuring rewards. If a reward fails to materialize there will be a prediction error.